CyberCode Academy

Course 17 - Computer Network Security Protocols And Techniques | Episode 9: Foundations of VPN Security: The IPsec Protocol Suite

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In this lesson, you’ll learn about:
  • The fundamentals of VPNs and IPsec
  • Key management and Security Associations (SA)
  • IPsec protocols: AH vs. ESP
  • Operational modes: Transport vs. Tunnel
1. VPNs and IPsec Fundamentals
  • A VPN (Virtual Private Network) creates a secure, logical tunnel over the public internet, allowing private communication without costly dedicated lines.
  • IPsec (Internet Protocol Security) operates at the network layer and supports both IPv4 and IPv6.
  • Security services provided by IPsec include:
    1. Access Control – Only authorized users can send/receive data
    2. Data Origin Authentication – Verify the source of the packet
    3. Integrity Protection – Ensure data hasn’t been tampered with
    4. Confidentiality – Encrypt the packet contents
    5. Anti-Replay – Detect and discard duplicated or malicious packets
2. IPsec Framework and Key Management
  • Encryption algorithms: DES, 3DES, AES for confidentiality
  • Integrity algorithms: MD5, SHA to create digital signatures (MACs)
  • Key exchange: Diffie-Hellman ensures a shared secret is established securely
3. Security Associations (SA) and IKE
  • An SA is a unidirectional logical connection, identified by:
    • SPI (Security Parameter Index)
    • Destination IP address
  • Bidirectional communication requires two SAs.
  • IKE (Internet Key Exchange) establishes SAs and manages keys:
    • IKE Phase 1: Creates a secure management tunnel (authenticates parties, negotiates algorithms, performs Diffie-Hellman exchange)
    • IKE Phase 2: Sets up the actual data tunnel (negotiates AH/ESP and operational mode)
  • IKEv2 is the modern version, supporting NAT traversal and keep-alive, and is widely used in 5G networks.
4. IPsec Protocols: AH vs. ESPProtocolSecurity ProvidedNotesAH (Authentication Header)Integrity & authenticationDoes not encrypt; ignores changing IP header fields like TTLESP (Encapsulating Security Payload)Integrity, authentication, encryptionPreferred protocol for most VPNs and mandatory for 5G

5. Operational Modes: Transport vs. Tunnel
  • Transport Mode: Only the payload is encrypted; original IP header is visible
  • Tunnel Mode: Entire original IP packet (header + payload) is encrypted inside a new IP packet
  • Most common setup: Tunnel Mode + ESP (encrypts everything and ensures privacy)
Analogy:
  • Transport Mode: Transparent envelope with coded letter inside – address is visible, content protected
  • Tunnel Mode: Envelope inside an opaque crate – both content and sender/receiver are hidden


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CyberCode AcademyBy CyberCode Academy